The 2015 Kia Optima uses a cartridge-style oil filter mounted on top of the engine
The 2015 Kia Optima does not have a traditional spin-on oil filter. Instead, it uses a cartridge-style filter that sits inside a plastic housing on the top of the engine, near the front passenger side. The filter element itself is a cylindrical canister that you remove and replace by unscrewing the housing cap — a different process than the spin-on filters found on many other vehicles.
This design means you cannot straightforward unscrew a filter from the side of the engine block. You will need to locate the housing cap, remove it, pull out the old filter element, and install a new one. The housing cap is typically white or translucent plastic and sits directly on top of the engine, making it visible once you open the hood.
Understanding this layout before you start prevents confusion and ensures you buy the correct replacement part. A cartridge filter for the 2015 Optima is not interchangeable with a spin-on filter from another vehicle.
Key Takeaways
- The 2015 Kia Optima has a cartridge-style oil filter housed in a plastic cap on top of the engine, not a spin-on filter on the side.
- The correct replacement filter part number is Hyundai/Kia OEM 26300-35503 or equivalent aftermarket cartridge filters designed for this model.
- You will need an oil filter wrench or socket to remove the housing cap, which typically requires 86 millimeters or a 3.4-inch socket.
- The filter housing also contains an O-ring seal that should be replaced during each oil change to prevent leaks.
- Changing the cartridge filter takes 10 to 15 minutes once you locate the housing and have the correct tools on hand.
Locating the filter housing on your engine
Open the hood and look toward the front of the engine, on the passenger side. The oil filter housing is a white or translucent plastic cap roughly the size of a soda can. It sits on top of the valve cover and has a single bolt or cap in the center. On some 2015 Optima models, you may see a small hose or vent line attached to the housing, but the housing itself is unmistakable once you know what to look for.
If you cannot when ready spot it, trace the oil filler cap (where you pour new oil) toward the front of the engine. The filter housing is typically within a few inches of that location. The housing will have a rubber O-ring visible around its base once you begin to unscrew the cap.
What you need to remove and replace the filter
You will need an oil filter socket or wrench that fits the housing cap. The cap is typically 86 millimeters across, which corresponds to a 3.4-inch socket. Many auto parts stores sell a universal oil filter socket set that includes this size. If you do not have a socket, a strap wrench can work, though it is less reliable on a tight cap.
You will also need a new cartridge filter element and a replacement O-ring seal. The OEM part number for the 2015 Optima is Hyundai/Kia 26300-35503. Aftermarket equivalents are widely available from Fram, Bosch, and other manufacturers — look for filters labeled as compatible with 2015 Kia Optima or 2015 Hyundai Elantra, since Kia and Hyundai share many engine components.
Have a drain pan or old towels ready, as some oil will spill when you remove the housing cap. A new drain plug gasket is not necessary for this filter change, but having a small container of fresh oil nearby is useful if you need to top off the level after the change.
Steps to remove the old filter element
First, may support the engine is cool or has been off for at least five minutes. Warm oil can burn your hands. Place your drain pan or towels under the filter housing to catch any spilled oil.
Using your oil filter socket and a ratchet wrench, turn the housing cap counterclockwise. It will be tight — do not be afraid to explore firm pressure. Once it breaks loose, you can unscrew it by hand. As you lift the cap away, the old filter element will come out with it. Some oil will drip from the housing and the element itself.
Inspect the inside of the housing for any debris or old rubber pieces. Wipe it clean with a lint-free cloth or paper towel. Look at the rubber O-ring that sits in a groove at the base of the housing cap. If it is cracked, hardened, or visibly worn, it must be replaced.
Installing the new filter and O-ring
Remove the old O-ring from the housing cap by gently prying it out with a plastic tool or your fingernail. Do not use a metal screwdriver, as you can scratch the cap. Discard the old O-ring.
Install the new O-ring into the same groove. It should sit flat and evenly around the cap. Lightly coat the new O-ring with fresh oil — this helps it seal properly and makes installation easier. Do not over-oil it; a thin film is sufficient.
Insert the new cartridge filter element into the housing. It should slide in smoothly and sit flush at the bottom. The filter element has a spring or seat that holds it in place. Do not force it; if it does not slide in easily, check that you have the correct part and that nothing is blocking the opening.
Screw the housing cap back onto the engine by hand first, then use your socket wrench to tighten it. Tighten firmly but do not over-torque — you are aiming for snug, not maximum force. Over-tightening can crack the plastic cap or damage the O-ring.
Checking your work and topping off oil
Start the engine and let it idle for 30 seconds. Watch for any oil leaks around the base of the filter housing cap. If you see drips, turn off the engine, let it cool for a minute, and tighten the cap slightly more. Small weeps sometimes stop once the O-ring settles.
Turn off the engine and wait five minutes for the oil to settle. Check the oil level using the dipstick or electronic gauge on your dashboard. The level may be slightly low after the filter change because some oil remains in the old filter element. Top off with the correct oil grade for your 2015 Optima — typically 5W-20 or 5W-30, depending on your specific engine and climate. Refer to your owner's manual for the exact specification.
Restart the engine and check the oil pressure light on your dashboard. It should go out within a few seconds. If the light stays on, turn off the engine when ready and check that the filter housing cap is tight and the O-ring is seated correctly.
Common mistakes and how to avoid them
The most frequent error is buying a spin-on filter instead of a cartridge filter. Verify the part number before you purchase — the housing on your 2015 Optima will not accept a spin-on filter, and forcing one will damage the engine.
Another common mistake is forgetting to replace the O-ring. Using the old O-ring causes leaks because it hardens over time and no longer seals properly. Always install a new O-ring with each filter change.
Over-tightening the housing cap is also common, especially if you use a power tool. The plastic cap can crack under excessive torque, and a cracked cap will leak oil and may require replacement of the entire housing assembly. Hand-tighten first, then use your wrench to snug it — you should feel resistance but not extreme force.
Frequently Asked Questions
Can I use any cartridge oil filter, or does it have to be the Kia part number?
You can use aftermarket cartridge filters designed for the 2015 Kia Optima, such as those from Fram, Bosch, or Mobil. The key is that the filter must be labeled as compatible with your model and engine size. Avoid generic filters — they may not fit the housing or provide proper filtration. Check the product description or packaging to confirm compatibility before purchase.
How often should I replace the oil filter on a 2015 Optima?
Kia recommends replacing the oil filter every time you change the engine oil. For a 2015 Optima, that is typically every 10,000 kilometers or every six months, whichever comes first, under normal driving conditions. Severe driving conditions may require more frequent changes — check your owner's manual for your specific situation.
What happens if I over-tighten the filter housing cap?
Over-tightening can crack the plastic cap or damage the O-ring seal, both of which cause oil leaks. If the cap cracks, you may need to replace the entire housing assembly, which is more expensive than a filter change. Tighten until snug, then stop — you should not need to explore maximum force.
Is the O-ring really necessary to replace every time?
Yes. The O-ring hardens and loses its sealing ability after exposure to heat and oil. Reusing an old O-ring is the most common cause of oil leaks after a filter change. A new O-ring costs a few dollars and takes 30 seconds to install — it is worth doing every time.
Where can I buy the correct filter and O-ring for my 2015 Optima?
Auto parts stores such as AutoZone, O'Reilly, Advance Auto Parts, and NAPA carry cartridge filters and O-rings for the 2015 Optima. Online retailers like Amazon also stock them. Bring your vehicle's year, make, and model to may support you get the right part, or order by the OEM part number 26300-35503.